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I bought a set of used M68 wheels and tires (17" for those that are not familiar with the style). Tires are Kuhmo MX (235F/255R).
I had 16" before so I knew that the ride would be a little firmer but it actually feels quite a bit firmer. I wondering if it's because the side walls on the Kuhmos might be stiffer as well.
Any thoughts?

A little offtopic, but I set my pressures kind of high (I think 33 and 36) but it was cold and now they're probably at 35/38. Gives me less traction and better fuel mileage right? I was surprised it started slipping at ~75km/h on the wilson heights north ramp off allen rd.

A little offtopic, but I set my pressures kind of high (I think 33 and 36) but it was cold and now they're probably at 35/38. Gives me less traction and better fuel mileage right? I was surprised it started slipping at ~75km/h on the wilson heights north ramp off allen rd.

35/38 shouldn't be enough to make any real difference in performance, at anything under 10/10ths track/autox driving.

BTW, IIRC you're running 235/40/17s? The minimum pressure for those actually is 33/36, as I just set mine to that as per the door plaque.

Hmm when I looked at my door panel ratings, they were so low...and I don't quite understand what it's trying to say with load and such.

I know what you mean, I think 235/40 looks so much better and is a lot easier to fit.

Stick to the door panel ratings, seriously. Unless you're at a track/autox event, those pressures are actually good to run. Of course it depends on the tire too, for example if the stock tires are UHP summers and you put on all-seasons with soft sidewalls you're going to want to up the pressure slightly.